Gaseoline sulfur reduction in fluid catalytic cracking

ABSTRACT

The sulfur content of liquid cracking products, especially the cracked gasoline, of the catalytic cracking process is reduced by the use of a sulfur reduction catalyst composition comprising a porous molecular sieve which contains a metal in an oxidation state above zero within the interior of the pore structure of the sieve as well as a rare earth component which enhances the cracking activity of the cracking catalyst. The molecular sieve is normally a faujasite such as USY. The primary sulfur reduction component is normally a metal of Period 3 of the Periodic Table, preferably vanadium. The rare earth component preferably includes cerium which enhances the sulfur reduction activity of the catalyst. The sulfur reduction catalyst may be used in the form of a separate particle additive or as a component of an integrated cracking/sulfur reduction catalyst.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to application Ser. No. 09/144,607,filed Aug. 31 1998.

[0002] Application Serial No. 09/______, filed concurrently (Mobil IPCase No. 10201-1, PL 98-76) describes catalyst compositions for thereduction of sulfur in gasolines based on large pore zeolites,especially zeolite USY which contain vanadium and cerium.

FIELD OF THE INVENTION

[0003] This invention relates to the reduction of sulfur in gasolinesand other petroleum products produced by the catalytic cracking process.The invention provides a catalytic composition for reducing productsulfur and a process for reducing the product sulfur using thiscomposition.

BACKGROUND OF THE INVENTION

[0004] Catalytic cracking is a petroleum refining process which isapplied commercially on a very large scale, especially in the UnitedStates where the majority of the refinery gasoline blending pool isproduced by catalytic cracking, with almost all of this coming from thefluid catalytic cracking (FCC) process. In the catalytic crackingprocess heavy hydrocarbon fractions are converted into lighter productsby reactions taking place at elevated temperature in the presence of acatalyst, with the majority of the conversion or cracking occurring inthe vapor phase. The feedstock is so converted into gasoline, distillateand other liquid cracking products as well as lighter gaseous crackingproducts of four or less carbon atoms per molecule. The gas partlyconsists of olefins and partly of saturated hydrocarbons.

[0005] During the cracking reactions some heavy material, known as coke,is deposited onto the catalyst. This reduces its catalytic activity andregeneration is desired. After removal of occluded hydrocarbons from thespent cracking catalyst, regeneration is accomplished by burning off thecoke and then the catalyst activity is restored. The threecharacteristic steps of the catalytic cracking can be therefore bedistinguished: a cracking step in which the hydrocarbons are convertedinto lighter products, a stripping step to remove hydrocarbons adsorbedon the catalyst and a regeneration step to burn off coke from thecatalyst. The regenerated catalyst is then reused in the cracking step.

[0006] Catalytic cracking feedstocks normally contain sulfur in the formof organic sulfur compounds such as mercaptans, sulfides and thiophenes.The products of the cracking process correspondingly tend to containsulfur impurities even though about half of the sulfur is converted tohydrogen sulfide during the cracking process, mainly by catalyticdecomposition of non-thiophenic sulfur compounds. The distribution ofsulfur in the cracking products is dependent on a number of factorsincluding feed, catalyst type, additives present, conversion and otheroperating conditions but, in any event a certain proportion of thesulfur tends to enter the light or heavy gasoline fractions and passesover into the product pool. With increasing environmental regulationbeing applied to petroleum products, for example in the ReformulatedGasoline (RFG) regulations, the sulfur content of the products hasgenerally been decreased in response to concerns about the emissions ofsulfur oxides and other sulfur compounds into the air followingcombustion processes.

[0007] One approach has been to remove the sulfur from the FCC feed byhydrotreating before cracking is initiated. While highly effective, thisapproach tends to be expensive in terms of the capital cost of theequipment as well as operationally since hydrogen consumption is high.Another approach has been to remove the sulfur from the cracked productsby hydrotreating. Again, while effective, this solution has the drawbackthat valuable product octane may be lost when the high octane olefinsare saturated.

[0008] From the economic point of view, it would be desirable to achievesulfur removal in the cracking process itself since this wouldeffectively desulfurize the major component of the gasoline blendingpool without additional treatment. Various catalytic materials have beendeveloped for the removal of sulfur during the FCC process cycle but, sofar, most developments have centered on the removal of sulfur from theregenerator stack gases. An early approach developed by Chevron usedalumina compounds as additives to the inventory of cracking catalyst toadsorb sulfur oxides in the FCC regenerator; the adsorbed sulfurcompounds which entered the process in the feed were released ashydrogen sulfide during the cracking portion of the cycle and passed tothe product recovery section of the unit where they were removed. SeeKrishna et al, Additives Improve FCC Process, Hydrocarbon Processing,November 1991, pages 59-66. The sulfur is removed from the stack gasesfrom the regenerator but product sulfur levels are not greatly affected,if at all.

[0009] An alternative technology for the removal of sulfur oxides fromregenerator removal is based on the use of magnesium-aluminum spinels asadditives to the circulating catalyst inventory in the FCCU. Under thedesignation DESOX™ used for the additives in this process, thetechnology has achieved a notable commercial success. Exemplary patentson this type of sulfur removal additive include U.S. Pat. Nos.4,963,520; 4,957,892; 4,957,718; 4,790,982 and others. Again, however,product sulfur levels are not greatly reduced.

[0010] A catalyst additive for the reduction of sulfur levels in theliquid cracking products is proposed by Wormsbecher and Kim in U.S. Pat.Nos. 5,376,608 and 5,525,210, using a cracking catalyst additive of analumina-supported Lewis acid for the production of reduced-sulfurgasoline but this system has not achieved significant commercialsuccess. The need for an effective additive for reducing the sulfurcontent of liquid catalytic cracking products has therefore persisted.

[0011] In application Ser. No. 09/144,607, filed Aug. 31 1998, we havedescribed catalytic materials for use in the catalytic cracking processwhich are capable of reducing the sulfur content of the liquid productsof the cracking process. These sulfur reduction catalysts comprise, inaddition to a porous molecular sieve component, a metal in an oxidationstate above zero within the interior of the pore structure of the sieve.The molecular sieve is in most cases a zeolite and it may be a zeolitehaving characteristics consistent with the large pore zeolites such aszeolite beta or zeolite USY or with the intermediate pore size zeolitessuch as ZSM-5. Non-zeolitic molecular sieves such as MeAPO-5, MeAPSO-5,as well as the mesoporous crystalline materials such as MCM-41 may beused as the sieve component of the catalyst. Metals such as vanadium,zinc, iron, cobalt, and gallium were found to be effective for thereduction of sulfur in the gasoline, with vanadium being the preferredmetal. When used as a separate particle additive catalyst, thesematerials are used in combination with the active catalytic crackingcatalyst (normally a faujasite such as zeolite Y, especially as zeoliteUSY) to process hydrocarbon feedstocks in the fluid catalytic cracking(FCC) unit to produce low-sulfur. Since the sieve component of thesulfur reduction catalyst may itself be an active cracking catalyst, forinstance, zeolite USY, it is also possible to use the sulfur reductioncatalyst in the form of an integrated cracking/sulfur reduction catalystsystem, for example, comprising USY as the active cracking component andthe sieve component of the sulfur reduction system together with addedmatrix material such as silica, clay and the metal, e.g. vanadium, whichprovides the sulfur reduction functionality.

[0012] Another consideration in the manufacture of FCC catalysts hasbeen catalyst stability, especially hydrothermal stability sincecracking catalysts are exposed during use to repeated cycles ofreduction (in the cracking step) followed by stripping with steam andthen by oxidative regeneration which produces large amounts of steamfrom the combustion of the coke, a carbon-rich hydrocarbon, which isdeposited on the catalyst particles during the cracking portion of thecycle. Early in the development of zeolitic cracking catalysts it wasfound that a low sodium content was required not only for optimumcracking activity but also for stability and that the rare earthelements such as cerium and lanthanum conferred greater hydrothermalstability. See, for example, Fluid Catalytic Cracking with ZeoliteCatalysts, Venuto et al., Marcel Dekker, N.Y., 1979, ISBN 0-8247-6870-1.

SUMMARY OF THE INVENTION

[0013] We have now developed catalytic materials for use in thecatalytic cracking process which are capable of improving the reductionin the sulfur content of the liquid products of the cracking processincluding, in particular, the gasoline and middle distillate crackingfractions. The present sulfur reduction catalyst are similar to the onesdescribed in application Ser. No. 09/144,607 in that a metal componentin an oxidation state above zero is present in the pore structure of amolecular sieve component of the catalyst composition, with preferenceagain being given to vanadium. In the present case, however, thecomposition also comprises one or more rare earth elements. We havefound that the presence of the rare earth component enhances thestability of the catalyst, as compared to the catalysts which containonly vanadium or another metal component and that in certain favorablecases, the sulfur reduction activity is also increased by the presenceof the rare earth elements. This is surprising since the rare earthcations in themselves have no sulfur reduction activity.

[0014] The present sulfur reduction catalysts may be used in the form ofan additive catalyst in combination with the active cracking catalyst inthe cracking unit, that is, in combination with the conventional majorcomponent of the circulating cracking catalyst inventory which isusually a matrixed, zeolite containing catalyst based on a faujasitezeolite, usually zeolite Y. Alternatively, they may be used in the formof an integrated cracking/ product sulfur reduction catalyst system.

[0015] According to the present invention, the sulfur removal catalystcomposition comprises a porous molecular sieve that contains (i) a metalin an oxidation state above zero within the interior of the porestructure of the sieve and (ii) a rare earth component. The molecularsieve is in most cases a zeolite and it may be a zeolite havingcharacteristics consistent with the large pore zeolites such as zeolitebeta or zeolite USY or with the intermediate pore size zeolites such asZSM-5. Non-zeolitic molecular sieves such as MeAPO-5, MeAPSO-5, as wellas the mesoporous crystalline materials such as MCM-41 may be used asthe sieve component of the catalyst. Metals such as vanadium, zinc,iron, cobalt, and gallium are effective. If the selected sieve materialhas sufficient cracking activity, it may be used as the active catalyticcracking catalyst component (normally a faujasite such as zeolite Y) or,alternatively, it may be used in addition to the active crackingcomponent, whether or not it has any cracking activity of itself. Thepresent compositions are useful to process hydrocarbon feedstocks influid catalytic cracking (FCC) units to produce low-sulfur gasoline andother liquid products, for example, light cycle oil that can be used asa low sulfur diesel blend component or as heating oil.

[0016] While the mechanism by which the metal-containing zeolitecatalyst compositions remove the sulfur components normally present incracked hydrocarbon products is not precisely understood, it doesinvolve the conversion of organic sulfur compounds in the feed toinorganic sulfur so that the process is a true catalytic process. Inthis process, it is believed that a zeolite or other molecular sieveprovides shape selectivity with varying pore size, and the metal sitesin zeolite provide adsorption sites for the sulfur species.

DRAWINGS

[0017] The drawings are graphs which show the performance of the presentsulfur reduction compositions as described below.

DETAILED DESCRIPTION

[0018] FCC Process

[0019] The present sulfur removal catalysts are used as a catalyticcomponent of the circulating inventory of catalyst in the catalyticcracking process, which these days is almost invariably the fluidcatalytic cracking (FCC) process. For convenience, the invention will bedescribed with reference to the FCC process although the presentadditives could be used in the older moving bed type (TCC) crackingprocess with appropriate adjustments in particle size to suit therequirements of the process. Apart from the addition of the presentadditive to the catalyst inventory and some possible changes in theproduct recovery section, discussed below, the manner of operating theprocess will remain unchanged. Thus, conventional FCC catalysts may beused, for example, zeolite based catalysts with a faujasite crackingcomponent as described in the seminal review by Venuto and Habib, FluidCatalytic Cracking with Zeolite Catalysts, Marcel Dekker, N.Y. 1979,ISBN 0-8247-6870-1 as well as in numerous other sources such asSadeghbeigi, Fluid Catalytic Cracking Handbook, Gulf Publ. Co. Houston,1995, ISBN 0-88415-290-1.

[0020] Somewhat briefly, the fluid catalytic cracking process in whichthe heavy hydrocarbon feed containing the organosulfur compounds will becracked to lighter products takes place by contact of the feed in acyclic catalyst recirculation cracking process with a circulatingfluidizable catalytic cracking catalyst inventory consisting ofparticles having a size ranging from about 20 to about 100 microns. Thesignificant steps in the cyclic process are:

[0021] (i) the feed is catalytically cracked in a catalytic crackingzone, normally a riser cracking zone, operating at catalytic crackingconditions by contacting feed with a source of hot, regenerated crackingcatalyst to produce an effluent comprising cracked products and spentcatalyst containing coke and strippable hydrocarbons;

[0022] (ii) the effluent is discharged and separated, normally in one ormore cyclones, into a vapor phase rich in cracked product and a solidsrich phase comprising the spent catalyst;

[0023] (iii) the vapor phase is removed as product and fractionated inthe FCC main column and its associated side columns to form liquidcracking products including gasoline,

[0024] (iv) the spent catalyst is stripped, usually with steam, toremove occluded hydrocarbons from the catalyst, after which the strippedcatalyst is oxidatively regenerated to produce hot, regenerated catalystwhich is then recycled to the cracking zone for cracking furtherquantities of feed.

[0025] In the present process, the sulfur content of the gasolineportion of the liquid cracking products, is effectively brought to lowerand more acceptable levels by carrying out the catalytic cracking in thepresence of the sulfur reduction catalyst.

[0026] FCC Cracking Catalyst

[0027] The present sulfur reduction catalyst compositions may be used inthe form of a separate particle additive which is added to the maincracking catalyst in the FCCU or, alternatively, they may be used ascomponents of the cracking catalyst to provide an integratedcracking/sulfur reduction catalyst system. The cracking component of thecatalyst which is conventionally present to effect the desired crackingreactions and the production of lower boiling cracking products, isnormally based on a faujasite zeolite active cracking component, whichis conventionally zeolite Y in one of its forms such as calcinedrare-earth exchanged type Y zeolite (CREY), the preparation of which isdisclosed in U.S. Pat. No. 3,402,996, ultrastable type Y zeolite (USY)as disclosed in U.S. Pat. No. 3,293,192, as well as various partiallyexchanged type Y zeolites as disclosed in U.S. Patents Nos. 3,607,043and 3,676,368. Cracking catalysts such as these are widely available inlarge quantities from various commercial suppliers. The active crackingcomponent is routinely combined with a matrix material such as silica oralumina as well as a clay in order to provide the desired mechanicalcharacteristics (attrition resistance etc.) as well as activity controlfor the very active zeolite component or components. The particle sizeof the cracking catalyst is typically in the range of 10 to 100 micronsfor effective fluidization. If used as a separate particle additive, thesulfur reduction catalyst (and any other additive) is normally selectedto have a particle size and density comparable to that of the crackingcatalyst so as to prevent component separation during the crackingcycle.

[0028] Sulfur Reduction System—Sieve Component

[0029] According to the present invention, the sulfur removal catalystcomprises a porous molecular sieve which contains a metal in anoxidation state above zero within the interior of the pore structure ofthe sieve. The molecular sieve is in most cases a zeolite and it may bea zeolite having characteristics consistent with the large pore zeolitessuch as zeolite Y, preferably as zeolite USY, or zeolite beta or withthe intermediate pore size zeolites such as ZSM-5, with the former classbeing preferred.

[0030] The molecular sieve component of the present sulfur reductioncatalysts may, as noted above, be a zeolite or a non-zeolitic molecularsieve. When used, zeolites may be selected from the large pore sizezeolites or intermediate pore zeolites (see Shape Selective Catalysis inIndustrial Applications, Chen et al, Marcel Dekker Inc., N.Y. 1989, ISBN0-8247-7856-1, for a discussion of zeolite classifications by pore sizeaccording to the basic scheme set out by Frilette et al in J. Catalysis67, 218-222 (1981)). The small pore size zeolites such as zeolite A anderionite, besides having insufficient stability for use in the catalyticcracking process, will generally not be preferred because of theirmolecular size exclusion properties which will tend to exclude thecomponents of the cracking feed as well as many components of thecracked products. The pore size of the sieve does not, however, appearto be critical since, as shown below, both medium and large pore sizezeolites have been found to be effective, as have the mesoporouscrystalline materials such as MCM-41.

[0031] Zeolites having properties consistent with the existence of alarge pore (12 ring) structure which may be used to make the presentsulfur reduction catalysts include zeolites Y in its various forms suchas Y, REY, CREY, USY, of which the last is preferred, as well as otherzeolites such as zeolite L, zeolite beta, mordenite includingde-aluminated mordenite, and zeolite ZSM-18. Generally, the large poresize zeolites are characterized by a pore structure with a ring openingof at least 0.7 nm and the medium or intermediate pore size zeoliteswill have a pore opening smaller than 0.7 nm but larger than about 0.56nm. Suitable medium pore size zeolites which may be used include thepentasil zeolites such as ZSM-5, ZSM-22, ZSM-23, ZSM-35, ZSM-50, ZSM-57,MCM-22, MCM-49, MCM-56 all of which are known materials. Zeolites may beused with framework metal elements other than aluminum, for example,boron, gallium, iron, chromium.

[0032] The use of zeolite USY is particularly desirable since thiszeolite is typically used as the active cracking component of thecracking catalyst and it is therefore possible to use the sulfurreduction catalyst in the form of an integrated cracking/sulfurreduction catalyst system. The USY zeolite used for the crackingcomponent may also, to advantage, be used as the sieve component for aseparate particle additive catalyst as it will continue to contribute tothe cracking activity of the overall catalyst present in the unit.Stability is correlated with low unit cell size with USY and, foroptimum results, the UCS for the USY zeolite in the finished catalystshould be from 2.420 to 2.455 nm, preferably 2.420 to 2.445 nm, with therange of 2.435 to 2.440 nm being very suitable. After exposure to therepeated steaming of the FCC cycles, further reductions in UCS will takeplace to a final value which is normally within the range of 2.420 to2.430 nm

[0033] In addition to the zeolites, other molecular sieves may be usedalthough they may not be as favorable since it appears that some acidicactivity (conventionally measured by the alpha value) is required foroptimum performance. Experimental data indicate that alpha values inexcess of about 10 (sieve without metal content) are suitable foradequate desulfurization activity, with alpha values in the range of 0.2to 2,000 being normally suitable¹. Alpha values from 0.2 to 300represent the normal range of acidic activity for these materials whenused as additives. 6 The alpha test is a convenient method of measuringthe overall acidity, inclusive of both its internal and externalacidity, of a solid material such as a molecular sieve. The test isdescribed in U.S. Pat. No.3,354,078; in the Journal of Catalysis, Vol.4,p.527 (1965); Vol. 6, p.278 (1966); and Vol. 61, p. 395 (1980). Alphavalues reported in this specification are measured at a constanttemperature of 538° C.

[0034] Exemplary non-zeolitic sieve materials which may provide suitablesupport components for the metal component of the present sulfurreduction catalysts include silicates (such as the metallosilicates andtitanosilicates) of varying silica-alumina ratios, metalloaluminates(such as germaniumaluminates), metallophosphates, aluminophosphates suchas the silico- and metalloaluminophosphates referred to as metalintegrated aluminophosphates (MeAPO and ELAPO), metal integratedsilicoaluminophosphates (MeAPSO and ELAPSO), silicoaluminophosphates(SAPO), gallogermanates and combinations of these. A discussion on thestructural relationships of SAPO's, AIPO's, MeAPO's, and MeAPSO's may befound in a number of resources including Stud. Surf. Catal. 37 13-27(1987). The AIPO's contain aluminum and phosphorus, whilst in the SAPO'ssome of the phosphorus and/or some of both phosphorus and aluminum isreplaced by silicon. In the MeAPO's various metals are present, such asLi, B, Be, Mg, Ti, Mn, Fe, Co, An, Ga, Ge, and As, in addition toaluminum and phosphorus, whilst the MeAPSO's additionally containsilicon. The negative charge of the Me_(a)Al_(b)P_(c)Si_(d)O_(e) latticeis compensated by cations, where Me is magnesium, manganese, cobalt,iron and/or zinc. Me_(x)APSO's are described in U.S. Pat. No. 4,793,984.SAPO-type sieve materials are described in U.S. Pat. No. 4,440,871;MeAPO type catalysts are described in U.S. Pat. Nos. 4,544,143 and4,567,029; ELAPO catalysts are described in U.S. Pat. No. 4,500,651, andELAPSO catalysts are described in European Patent Application 159,624.Specific molecular sieves are described, for example, in the followingpatents: MgAPSO or MAPSO-U.S. Pat. No. 4,758,419. MnAPSO-U.S. Pat. No.4,686,092; CoAPSO-U.S. Pat. No. 4,744,970; FeAPSO-U.S. Pat. No.4,683,217 and ZnAPSO U.S. Pat. No. 4,935,216. Specificsilicoaluminophosphates which may be used include SAPO-11, SAPO-17,SAPO-34, SAPO-37; other specific sieve materials include MeAPO-5,MeAPSO-5.

[0035] Another class of crystalline support materials which may be usedis the group of mesoporous crystalline materials exemplified by theMCM-41 and MCM-48 materials. These mesoporous crystalline materials aredescribed in U.S. Pat. Nos. 5,098,684; 5,102,643; and 5,198,203. MCM-41,which is described in U.S. Pat. No. 5,098,684, is characterized by amicrostructure with a uniform, hexagonal arrangement of pores withdiameters of at least about 1.3 nm: after calcination it exhibits anX-ray diffraction pattern with at least one d-spacing greater than about1.8 nm and a hexagonal electron diffraction pattern that can be indexedwith a d100 value greater than about 1.8 nm which corresponds to thed-spacing of the peak in the X-ray diffraction pattern. The preferredcatalytic form of this material is the aluminosilicate although othermetallosilicates may also be utilized. MCM-48 has a cubic structure andmay be made by a similar preparative procedure.

[0036] Metal Components

[0037] Two metal components are incorporated into the molecular sievesupport material to make up the present catalytic compositions. Onecomponent is a rare earth such as lanthanum or a mixture of rare earthelements such as cerium and lanthanum. The other metal component can beregarded as the primary sulfur reduction component although the mannerin which it effects sulfur reduction is not clear, as discussed inapplication Ser. No. 09/144,607, to which reference is made for adescription of sulfur reduction catalyst compositions containingvanadium and other metal components effective for this purpose. Forconvenience this component of the composition will be referred to inthis application as the primary sulfur reduction component. In order tobe effective, this metal (or metals) should be present inside the porestructure of the sieve component. Metal-containing zeolites and othermolecular sieves can be prepared by (1) post-addition of metals to thesieve or to a catalyst containing the sieve(s), (2) synthesis of thesieve(s) containing metal atoms in the framework structure, and by (3)synthesis of the sieve(s) with trapped, bulky metal ions in the zeolitepores. Following addition of the metal component, washing to removeunbound ionic species and drying and calcination should be performed.These techniques are all known in themselves. Post-addition of the metalions is preferred for simplicity and economy, permitting available sievematerials to be converted to use for the present additives. A widevariety of post-addition methods of metals can be used to produce acatalyst of our invention, for example, aqueous exchange of metal ions,solid-state exchange using metal halide salt(s), impregnation with ametal salt solution, and vapor deposition of metals. In each case,however, it is important to carry out the metal(s) addition so that themetal component enters the pore structure of the sieve component.

[0038] It has been found that when the metal of the primary sulfurreduction component is present as exchanged cationic species in thepores of the sieve component, the hydrogen transfer activity of themetal component is reduced to the point that hydrogen transfer reactionstaking place during the cracking process will normally maintained at anacceptably low level with the preferred metal components. Thus, coke andlight gas make during cracking increase slightly but they remain withintolerable limits. Since the unsaturated light ends can be used in anyevent as alkylation feed and in this way recycled to the gasoline pool,there is no significant loss of gasoline range hydrocarbons incurred bythe use of the present additives.

[0039] Because of the concern for excessive coke and hydrogen makeduring the cracking process, the metals for incorporation into theadditives should not exhibit hydrogenation activity to a marked degree.For this reason, the noble metals such as platinum and palladium whichpossess strong hydrogenation-dehydrogenation functionality are notdesirable. Base metals and combinations of base metals with stronghydrogenation functionality such as nickel, molybdenum, nickel-tungsten,cobalt-molybdenum and nickel-molybdenum are not desirable for the samereason. The preferred base metals are the metals of Period 3, Groups 5,8, 9, 12, (IUPAC classification, previously Groups 2B, 5B and 8B) of thePeriodic Table. Vanadium, zinc, iron, cobalt, and gallium are effectivewith vanadium being the preferred metal component. It is surprising thatvanadium can be used in this way in an FCC catalyst composition sincevanadium is normally thought to have a very serious effect on zeolitecracking catalysts and much effort has been expended in developingvanadium suppressers. See, for example, Wormsbecher et al, VanadiumPoisoning of Cracking Catalysts: Mechanism of Poisoning and Design ofVanadium Tolerant Catalyst System, J. Catalysis 100, 130-137 (1986). Itis believed that the location of the vanadium inside the pore structureof the sieve immobilizes the vanadium and prevents it from becomingvanadic acid species which can combine deleteriously with the sievecomponent; in any event, the present zeolite-based sulfur reductioncatalysts containing vanadium as the metal component have undergonerepeated cycling between reductive and oxidative/steaming conditionsrepresentative of the FCC cycle while retaining the characteristiczeolite structure, indicating a different environment for the metal.

[0040] Vanadium is particularly suitable for gasoline sulfur reductionwhen supported on zeolite USY. The yield structure of the V/USY sulfurreduction catalyst is particularly interesting. While other zeolites,after metals addition, demonstrate gasoline sulfur reduction, they tendto convert gasoline to C₃ and C₄ gas. Even though much of the convertedC₃=and C₄=can be alkylated and re-blended back to the gasoline pool, thehigh C₄− wet gas yield may be a concern since many refineries arelimited by their wet gas compressor capacity. The metal-containing USYhas similar yield structure to current FCC catalysts; this advantagewould allow the V/USY zeolite content in a catalyst blend to be adjustedto a target desulfurization level without limitation from FCC unitconstraints. The vanadium on Y zeolite catalyst, with the zeoliterepresented by USY, is therefore a particularly favorable combinationfor gasoline sulfur reduction in FCC. The USY which has been found togive particularly good results is a USY with low unit cell size in therange from 2.420 to 2.450 nm, preferably 2.435 to 2.450 nm (followingtreatment) and a correspondingly low alpha value. Combinations of basemetals such as vanadium/zinc as the primary sulfur reduction componentmay also be favorable in terms of overall sulfur reduction.

[0041] The amount of the primary sulfur reduction metal component in thesulfur reduction catalyst is normally from 0.2 to 5 weight percent,typically 0.5 to 5 weight percent, (as metal, relative to weight ofsieve component) but amounts outside this range, for example, from 0.10to 10 weight percent may still be found to give some sulfur removaleffect. When the sieve is matrixed, the amount of the primary sulfurreduction metal component expressed relative to the total weight of thecatalyst composition will, for practical purposes of formulation,typically extend from 0.1 to 5, more typically from 0.2 to 2 weightpercent of the entire catalyst.

[0042] The second metal component of the sulfur reduction catalystcomposition comprises a rare earth metal or metals which is presentwithin the pore structure of the molecular sieve and is thought to bepresent in the form of cations exchanged onto the exchangeable sitespresent on the sieve component. The rare earth (RE) componentsignificantly improves the catalyst stability in the presence ofvanadium. For example, higher cracking activity can be achieved withRE+V/USY catalyst compared to a V/USY catalyst, while comparablegasoline sulfur reduction is obtained. Rare earths of the lanthanideseries from atomic number from 57 to 71 such as lanthanum, cerium,dysprosium, praseodymium, samarium, europium, gadolinium, ytterbium andlutetium may be used in this way but from the point of view ofcommercial availability, lanthanum and mixtures of cerium and lanthanumwill normally be preferred. In application Ser. No. 09______ , filedconcurrently with this application (Mobil IP Case 100 , PL 98-76), weshow that cerium is the most effective rare earth component from theviewpoint of sulfur reduction as well as catalyst stability.

[0043] The amount of rare earth is typically from 1 to 10 wt. percent ofthe catalyst composition, in most cases from 2 to 5 wt. percent.Relative to the weight of the sieve, the amount of the rare earth willnormally be from about 2 to 20 weight percent and in most cases from 4to 10 weight percent of the sieve, depending on the sieve:matrix ratio.

[0044] The rare earth component can suitably be incorporated into themolecular sieve component by exchange onto the sieve, either in the formof the unmatrixed crystal or of the matrixed catalyst. When thecomposition is being formulated with the preferred USY zeolite sieve, avery effective manner of incorporation is to add the rare earth ions tothe USY sieve (typically 2.445-2.465 nm unit cell size) followed byadditional steam calcination to lower the unit cell size of the USY to avalue typically in the range of 2.420 to 2.450 nm., after which theprimary metal component may be added if not already present. The USYshould have a low alkali metal (mainly sodium) content for stability aswell as for satisfactory cracking activity; this will normally besecured by the ammonium exchange made during the ultrastabilizationprocess to a desirable low sodium level of not more than 1 weightpercent, preferably not more than 0.5 weight percent, on the sieve.

[0045] The metal components are incorporated into the catalystcomposition in a way which ensures that they enter the interior porestructure of the sieve. The metals may be incorporated directly into thecrystal or into the matrixed catalyst. When using the preferred USYzeolite as the sieve component, this can suitably be done as describedabove, by recalcining a USY cracking catalyst containing the rare earthcomponent to ensure low unit cell size and then incorporating the metal,e.g. vanadium, by ion exchange or by impregnation under conditions whichpermit cation exchange to take place so that the metal ion isimmobilized in the pore structure of the zeolite. Alternatively, theprimary sulfur reduction component and the rare earth metal componentcan be incorporated into the sieve component, e.g. USY zeolite or ZSM-5crystal, after any necessary calcination to remove organics from thesynthesis after which the metal-containing component can be formulatedinto the finished catalyst composition by the addition of the crackingand matrix components and the formulation spray dried to form the finalcatalyst.

[0046] When the catalyst is being formulated as an integrated catalystsystem, it is preferred to use the active cracking component of thecatalyst as the sieve component of the sulfur reduction system,preferably zeolite USY, both for simplicity of manufacture but also forretention of controlled cracking properties. It is, however, possible toincorporate another active cracking sieve material such as zeolite ZSM-5into an integrated catalyst system and such systems may be useful whenthe properties of the second active sieve material are desired, forinstance, the properties of ZSM-5. The impregnation/exchange processshould in both cases be carried out with a controlled amount of metal sothat the requisite number of sites are left on the sieve to catalyze thecracking reactions which may be desired from the active crackingcomponent or any secondary cracking components which are present, e.g.ZSM-5.

[0047] Use of Sulfur Reduction Catalyst Composition

[0048] Normally the most convenient manner to use the sulfur reductioncatalyst will be as a separate particle additive to the catalystinventory. In its preferred form, with zeolite USY as the sievecomponent, the addition of the catalyst additive to the total catalystinventory of the unit will not result in significant reduction inoverall cracking because of the cracking activity of the USY zeolite.The same is true when another active cracking material is used as thesieve component. When used in this way, the composition may be used inthe form of the pure sieve crystal, pelleted (without matrix but withadded metal components) to the correct size for FCC use. Normally,however, the metal-containing sieve will be matrixed in order to achieveadequate particle attrition resistance and to maintain satisfactoryfluidization. Conventional cracking catalyst matrix materials such asalumina or silica-alumina, usually with added clay, will be suitable forthis purpose. The amount of matrix relative to the sieve will normallybe from 20:80 to 80:20 by weight. Conventional matrixing techniques maybe used.

[0049] Use as a separate particle catalyst additive permits the ratio ofsulfur reduction and cracking catalyst components to be optimizedaccording to the amount of sulfur in the feed and the desired degree ofdesulfurization; when used in this manner, it is typically used in anamount from 1 to 50 weight percent of the entire catalyst inventory inthe FCCU; in most cases the amount will be from 5 to 25 weight percent,e.g. 5 to 15 weight percent. About 10 percent represents a norm for mostpractical purposes. The additive may be added in the conventionalmanner, with make-up catalyst to the regenerator or by any otherconvenient method. The additive remains active for sulfur removal forextended periods of time although very high sulfur feeds may result inloss of sulfur removal activity in shorter times.

[0050] The alternative to the use of the separate particle additive isto use the sulfur reduction catalyst incorporated into the crackingcatalyst to form an integrated FCC cracking/gasoline sulfur reductioncatalyst. If the sulfur reduction metal components are used incombination with a sieve other than the active cracking component, forexample, on ZSM-5 or zeolite beta when the main active crackingcomponent is USY, the amount of the sulfur reduction component (sieveplus metals) will typically be up to 25 weight percent of the entirecatalyst or less, corresponding to the amounts in which it may be usedas a separate particle additive, as described above.

[0051] Other catalytically active components may be present in thecirculating inventory of catalytic material in addition to the crackingcatalyst and the sulfur removal additive. Examples of such othermaterials include the octane enhancing catalysts based on zeolite ZSM-5,CO combustion promoters based on a supported noble metal such asplatinum, stack gas desulfurization additives such as DESOX™ (magnesiumaluminum spinel), vanadium traps and bottom cracking additives, such asthose described in Krishna, Sadeghbeigi, op cit and Scherzer, OctaneEnhancing Zeolitic FCC Catalysts, Marcel Dekker, N.Y., 1990, ISBN0-8247-8399-9. These other components may be used in their conventionalamounts.

[0052] The effect of the present additives is to reduce the sulfurcontent of the liquid cracking products, especially the light and heavygasoline fractions although reductions are also noted in the light cycleoil, making this more suitable for use as a diesel or home heating oilblend component. The sulfur removed by the use of the catalyst isconverted to inorganic form and released as hydrogen sulfide which canbe recovered in the normal way in the product recovery section of theFCCU in the same way as the hydrogen sulfide conventionally released inthe cracking process. The increased load of hydrogen sulfide may imposeadditional sour gas/water treatment requirements but with thesignificant reductions in gasoline sulfur achieved, these are not likelyto be considered limitative.

[0053] Very significant reductions in gasoline sulfur can be achieved bythe use of the present catalysts, in some cases up to about 50% relativeto the base case using a conventional cracking catalyst, at constantconversion, using the preferred form of the catalyst described above.Gasoline sulfur reduction of 25% is readily achievable with many of theadditives according to the invention, as shown by the Examples below.The extent of sulfur reduction may depend on the original organic sulfurcontent of the cracking feed, with the greatest reductions achieved withthe higher sulfur feeds. The metals content of the equilibrium catalystin the unit may also affect the degree of desulfurization achieved, witha low metals content, especially vanadium content, on the equilibriumcatalyst favoring greater desulfurization. Desulfurization will be veryeffective with E-catalyst vanadium contents below 1,000 ppm although thepresent catalysts remain effective even at much higher vanadiumcontents. Sulfur reduction may be effective not only to improve productquality but also to increase product yield in cases where the refinerycracked gasoline end point has been limited by the sulfur content of theheavy gasoline fraction; by providing an effective and economical way toreduce the sulfur content of the heavy gasoline fraction, the gasolineend point may be extended without the need to resort to expensivehydrotreating, with a consequent favorable effect on refinery economics.Removal of the various thiophene derivatives which are refractory toremoval by hydrotreating under less severe conditions is also desirableif subsequent hydrotreatment is contemplated.

EXAMPLE 1 Preparation of Catalyst Series 1

[0054] All samples in Catalyst Series 1 were prepared from a singlesource of spray dried material, consisting of 50% USY, 21% silica soland 29% clay. The USY had a starting unit cell size of 2.454 nm,SiO₂/Al₂O₃ mol ratio of 5.46 and a total surface area of 810 m²g¹.

[0055] A V/USY catalyst, Catalyst A, was prepared by slurrying the abovespray dried catalyst with NH₄ OH at a pH of 6, followed by filtration,ammonium sulfate exchange and washing with water. The catalyst wascalcined in the presence of steam at 1300° F. for 2 hours andimpregnated with vanadyl oxalate. The steam calcination lowered the unitcell size of the zeolite and improved its stability in the presence ofvanadium.

[0056] A V/USY catalyst, Catalyst B, was prepared in the same way asCatalyst A, with the exception that the initial slurrying of thecatalyst was performed at a pH between 3.2 and 3.5.

[0057] Two RE+V/USY catalysts, Catalyst C and D were prepared in thesame way as Catalyst B, with the exception that after ammonium sulfateexchange the catalysts were exchanged with solutions of rare earthchloride to add 2 and 4 wt % RE₂O₃ onto the catalyst, respectively. Therare earth solution that was used had some of its Ce³⁺ extracted out,thus contains only a little Ce ions.

[0058] A Ce+V/USY catalyst, Catalyst E was prepared in the same way asCatalyst B, with the exception that after ammonium sulfate exchange thecatalyst was exchanged with a solution of cerium chloride to add 5%cerium (as CeO₂) onto the catalyst.

[0059] These catalysts were then steamed deactivated, to simulatecatalyst deactivation in an FCC unit, in a fluidized bed steamer at 770°C.(1420° F.) for 20 hours using 50% steam. The physical properties ofthe calcined and steam deactivated catalysts are summarized in Table 1.TABLE 1 Physical Properties of the V, RE + V, and Ce + V USY/ Silica SolCatalysts V/USY V/USY RE + V/USY RE + V/USY Ce + V/USY Cat. A Cat. BCat. C Cat. D Cat. E Calcined Cat. V loading, wt % 0.36 0.37 0.39 0.380.39 RE₂O₃ loading, wt % N.A. N.A. 2.0 4.1 5.1 Ce₂O₃, wt % N.A. N.A.0.49 0.95 4.95 La₂O₃, wt % N.A. N.A. 0.96 1.83 0.03 Na₂O, wt % 0.30 0.240.42 0.21 0.19 Unit cell size, nm 2.433 2.433 2.442 2.443 2.442Deactivated Cat. (CPS 770° C. 20 hrs) Surface area, m²g⁻¹ 255 252 249248 284 Unit cell size, nm 2.425 2.424 2.4.26 2.428 2.428

Example 2 Preparation of Catalyst Series 2

[0060] A V/USY catalyst, Catalyst F, was prepared using a USY zeolitewith a silica-to-alumina ratio of 5.4 and unit cell size of 2.435 nm. Afluid catalyst was prepared by spray drying an aqueous slurry containing50 wt % of the USY crystals in a silica sol/clay matrix. The matrixcontained 22-wt % silica sol and 28-wt % kaolin clay. The spray-driedcatalyst was exchanged with NH₄ ⁺ by an exchange with a solution ofammonium sulfate and then dried. Then the USY catalyst was impregnatedwith a solution of vanadium oxalate to target 0.5 wt % V.

[0061] A RE+V/USY catalyst, Catalyst G, was prepared using a USY zeolitewith a silica-to-alumina ratio of 5.5 and a unit cell size of 2.454 nm.The USY was exchanged with NH₄ ⁺ by an exchange with a solution ofammonium sulfate. The NH₄ ⁺ exchanged USY was then exchanged with rareearth cations (e.g., La³⁺, Ce³⁺, etc.) by exchange with a solution ofmixed rare earth chlorides. The rare earth solution that was used hadmost of its Ce³⁺ extracted out, thus contained very little Ce. TheRE-exchanged USY was further washed, dried, and calcined in the presenceof steam in a rotary calciner at 760° C. (1400° F.). The steamcalcination lowered the unit cell size of the zeolite to 24.40 Å andimproved its stability in the presence of vanadium. A fluid catalyst wasprepared by spray drying an aqueous slurry containing 50 wt % of theRE-USY crystals in a silica sol/clay matrix. The matrix contained 22-wt% silica sol and 28-wt % kaolin clay. The spray-dried catalyst wasexchanged with NH₄ ⁺ by an exchange with a solution of ammonium sulfateand was then dried and calcined at 540° C. (1000° F.) for 2 hours.Following calcination, the RE/USY catalyst was impregnated with a VOS0 ₄solution.

[0062] Catalyst H, was prepared using similar procedures as for CatalystG except a solution of mixed RECI₃ containing mostly CeCI₃ was used toexchange the USY. Catalyst H was prepared using a commercial USY zeolitewith a silica-to-alumina ratio of 5.5 and a unit cell size of 2.454 nm.The USY was exchanged with NH₄ ⁺ by an exchange with a solution ofammonium sulfate. The NH₄ ⁺-exchanged USY was then exchanged with asolution of CeCl₃ containing some lanthanum. The exchanged USY wasfurther washed, dried, and calcined in the presence of steam in a rotarycalciner at 760° C. (1400° F.). The steam calcination lowered the unitcell size of the zeolite to 2.440 nm. A fluid catalyst was prepared byspray drying an aqueous slurry containing 50 wt % of the rare earthcontaining USY crystals in a silica sol/clay matrix. The matrixcontained 22-wt % silica sol and 28-wt % kaolin clay. The spray-driedcatalyst was exchanged with NH₄ ⁺ by an exchange with a solution ofammonium sulfate and was then dried and calcined at 540° C. (1000° F.)for 2 hours. Following calcination, the catalyst was impregnated with aVOSO₄ solution. Physical properties of the calcined catalysts aresummarized in Table 2. TABLE 2 Physical Properties of V/USY, RE + V/USYSilica-Sol Catalysts V/USY RE + V/USY RE + V/USY Catalyst F Catalyst GCatalyst H Calcined Cat. V loading, wt % 0.5 0.43 0.44 RE₂O₃ loading, wt% N.A. 1.93 2.66 CeO₂ loading, wt % N.A. 0.21 2.42 Na₂O, wt % 0.13 0.160.20 Surface area, m²g⁻¹ 327 345 345 Unit cell size, nm 2.435 — —

[0063] The above additives were tested for gas oil cracking activity andselectivity using the ASTM microactivity test (ASTM procedure D-3907).Two vacuum gas oil feed stocks were used to test the catalysts, a 1%sulfur gas oil feed for testing of gasoline sulfur reduction and a 2.6%sulfur gas oil feed for testing of catalyst stability. Properties of thefeed stocks are shown in Table 3 below. A range of conversions wasobtained by varying the catalyst-to-oil ratios with the reactions run at527° C. (980° F.). The gasoline range product from each material balancewas analyzed with a sulfur GC (AED) to determine the gasoline sulfurconcentration. To reduce experimental errors in the sulfur concentrationassociated with fluctuations in distillation cut point of gasoline, thesulfur species ranging from thiophene to C₄-thiophenes in syncrude(excluding benzothiophene and higher boiling S species) were quantitatedand the sum was defined as “cut-gasoline S.” TABLE 3 Properties ofVacuum Gas Oil Feeds Vacuum Gas Oil Vacuum Gas Oil Charge StockProperties No. 1 No. 2 API Gravity 26.6 22.5 Aniline Point, C. 83 73CCR, wt % 0.23 0.25 Sulfur, wt % 1.05 2.59 Nitrogen, ppm 600 860 Basicnitrogen, ppm 310 340 Ni, ppm 0.32 — V, ppm 0.68 — Fe, ppm 9.15 — Cu,ppm 0.05 — Na, ppm 2.93 — Simulated Distillation, ° C. IBP, 181 217 50wt %, 380 402 99.5%, 610 553

EXAMPLE 3 FLUID CATALYTIC CRACKING EVALUATION OF SERIES 1 CATALYSTS

[0064] The catalysts from Example 1 were steam deactivated in afluidized bed steamer at 770° C. (1420° F.) for 20 hours using 50% steamand 50% gas. The gas stream was changed from air, N₂, propylene, and toN₂ for every ten minutes, then cycled back to air again to simulate thecoking/ regeneration cycle of a FCC unit (cyclic steaming). The steamdeactivation cycle was ended with air-burn (ending-oxidation).Twenty-five weight percent of steamed additive catalysts were blendedwith an equilibrium catalyst of very low metals level (120 ppm V and 60ppm Ni) from an FCC unit.

[0065] Performances of the catalysts are summarized in Table 4, wherethe product selectivity was interpolated to a constant conversion, 65 wt% conversion of feed to 220° C. or below (430° F.-) material. TABLE 4Catalytic Cracking Performance of Series 1 Catalysts +25% +25% +25% ECat+25% +25% RE + RE + RE + Base V/USY V/USY V/USY V/USY V/USY Case Cat ACat B Cat C Cat D Cat E MAT Product Yields Conversion, wt % 65 65 65 6565 65 Cat/Oil 3.0 3.3 3.3 2.9 3.0 2.9 H2 yield, wt % 0.03 +0.05 +0.05+0.04 +0.02 +0.04 C1 + C2 1.1 +0.1 +0.1 +0 +0.1 +0 Gas, wt % Total C3Gas, 4.3 +0.1 +0.1 −0.1 +0 −0.2 wt % C3 = yield, wt % 3.7 +0.1 +0.1 +0+0 −0.1 Total C4 Gas, 9.3 +0.1 +0.2 −0.1 +0 −0.3 wt % C4 = yield, wt %4.7 +0.3 +0.4 +0.4 +0.1 +0 C5 + 47.6 −0.6 −0.4 +0.4 +0 +0.5 Gasoline, wt% LFO, wt % 29.6 +0 +0.2 +0 +0.1 +0 HFO, wt % 5.4 +0 −0.2 +0 −0.1 +0Coke, wt % 2.4 +0.3 +0.0 −0.2 −0.1 −0.1 Cut Gasoline 618 377 366 369 382352 S, ppm % Reduction Base 39.0 40.8 40.4 38.3 43.1 in Cut Gasoline S

[0066] The cat-to-oil ratios in Table 4 show that the blends ofdeactivated V/USY and ECat require higher cat-to-oil ratio than the 100%ECat base case to achieve 65% conversion (3.3 vs. 3.0 Cat/Oil, i.e.,about 10% reduction in activity). It is due to lower cracking activityof V/USY catalysts relative to the ECat. In comparison, addition of theRE+V/USY catalysts did not increase the cat-to-oil ratio to achieve 65%conversion. These cat-to-oil results indicate that the RE+V/USYcatalysts are more stable and maintain their cracking activity betterthan the V/USY catalysts.

[0067] Compared to the ECat base case, addition of V/USY and RE+V/USYcatalyst made small changes in the overall product yield structure.There were slight increases in hydrogen and coke yields. Also a smallchanges in C₄-gas, gasoline, light cycle oil and heavy fuel oil yieldswere observed. Addition of the V/USY and RE+V/USY catalysts changed thegasoline S concentration substantially. When 25 wt % of each of CatalystA or B (V/USY reference catalysts) was blended with the equilibrium FCCcatalyst, 39.0 and 40.8% reduction in gasoline sulfur concentration wasachieved. When 25 wt % of RE/USY catalysts (Catalyst C and D) was addedto the ECat Catalyst, the gasoline sulfur reduction activities arecomparable to the reference catalysts (38-40%). The RE+V/ USY catalystcontaining mostly cerium as the rare earth metal (Catalyst E) gave a43.1% reduction in gasoline S, to reduce the gasoline S content by about4% additionally, i.e., 10% improvement over the V/USY and mixed RE/USYcatalysts. All catalysts have a comparable vanadium loading(0.36-0.39%).

[0068] These results show that addition of rare earths improves thecracking activity of a V/USY catalyst. Changes in the cracked productyields are minor. Among rare earth ions, cerium exhibits a uniqueproperty in that the Ce+V/USY catalyst not only exhibits higher crackingactivity but also exhibits increased gasoline sulfur reduction activityat fluid catalytic cracking conditions. The rare earth RE/USY catalystwithout major amounts of cerium has no added benefit over V/USY forgasoline S reduction whereas the presence of cerium further lowered thegasoline sulfur level of the V/USY or RE/USY (without major ceriumlevels) catalysts.

EXAMPLE 4 Comparison of Cracking Activity of Series 2 Catalysts.

[0069] The V and RE/V USY catalysts from Example 2 (Series 2 Catalysts)were steam deactivated at 790° C. (1420° F.) for various lengths of timeto compare catalyst stability. The catalysts were steamed in a fluidizedbed steamer for 2.3, 5.3, 10, 20, and 30 hours using 50% steam and 50%gas (cyclic steaming ending-reduction, as described above). The surfacearea retentions of the deactivated catalysts are plotted in FIG. 1.

[0070] The steam deactivated catalysts were tested for gas oil crackingactivity using an ASTM microactivity test (ASTM procedure D-3907) withVacuum Gas Oil No. 2 (above −2.6 wt % S). At a 30-second contact timeand at 545° C. (980° F.) reaction temperature, a weight percentconversion to 220° C.−(430° F.−) was measured at a constantcatalyst-to-oil ratio of 4:1. Conversions as a function of steamdeactivation time are plotted in FIG. 2.

[0071] The surface area retentions shown in FIG. 1 indicate that VIUSYand RE+V/USY catalysts show comparable surface area retention uponvarious hydrothermal deactivation conditions suggesting that all threecatalysts have comparable framework structure stability. However, theconversion plot shown in FIG. 2 clearly indicates that RE+V/USY havemuch improved cracking activity retention as severity of hydrothermaldeactivation increases. Upon the hydrothermal deactivation, theimprovement in cracking activity from the V/USY to RE+V version wasabout 15% conversion. No apparent differences were observed between theRE versions with varying amounts of cerium. These results are consistentwith that of Example 3 where RE+V/USY achieved the target conversion ata lower cat-to-oil ratio than V/USY. These conversion results indicatethat the RE+V/USY catalysts are more stable and maintain their crackingactivity better than the V/USY catalysts. The addition of rare earthions to the USY followed by steam calcination to lower the unit cellsize of the zeolite improved catalyst stability in the presence ofvanadium.

We claim:
 1. A method of reducing the sulfur content of a catalytically cracked petroleum fraction, which comprises catalytically cracking a petroleum feed fraction containing organosulfur compounds at elevated temperature in the presence of a cracking catalyst and a product sulfur reduction catalyst which comprises a porous molecular sieve having (i) a first metal component which is within the interior pore structure of the molecular sieve and which comprises a metal in an oxidation state greater than zero and (ii) a second metal component which is within the interior pore structure of the molecular sieve and which comprises at least one rare earth, to produce liquid cracking products of reduced sulfur content.
 2. A method according to claim 1 in which the product sulfur reduction catalyst comprises a large pore size or intermediate pore size zeolite as the molecular sieve component and, as the first metal component, at least one metal of Period 3, Groups 5, 8, 9 or 12 of the Periodic Table.
 3. A method according to claim 2 in which the large pore size zeolite comprises zeolite USY.
 4. A method according to claim 2 in which the first metal component comprises vanadium.
 5. A method according to claim 2 in which the second metal component comprises lanthanum alone or in combination with cerium.
 6. A method according to claim 1 in which the second metal component is present in an amount from 1 to 10 weight percent of the catalytic composition.
 7. A method according to claim 1 in which the product sulfur reduction catalyst comprises a USY zeolite having a UCS of from 2.420 to 2.455 nm, a bulk silica:alumina ratio of at least 5.0 as the molecular sieve component and, as the first metal component, at least one of zinc or vanadium in an oxidation state greater than zero and, as the second metal component, a combination of lanthanum and cerium.
 8. A method according to claim 1 in which the sulfur reduction catalyst is a separate particle additive catalyst.
 9. In a fluid catalytic cracking process in which a heavy hydrocarbon feed comprising organosulfur compounds is catalytically cracked to lighter products by contact in a cyclic catalyst recirculation cracking process with a circulating fluidizable catalytic cracking catalyst inventory consisting of particles having a size ranging from about 20 to about 100 microns, comprising: (i) catalytically cracking the feed in a catalytic cracking zone operating at catalytic cracking conditions by contacting feed with a source of regenerated cracking catalyst to produce a cracking zone effluent comprising cracked products and spent catalyst containing coke and strippable hydrocarbons; (ii) discharging and separating the effluent mixture into a cracked product rich vapor phase and a solids rich phase comprising spent catalyst; (iii) removing the vapor phase as a product and fractionating the vapor to form liquid cracking products including gasoline, (iv) stripping the solids rich spent catalyst phase to remove occluded hydrocarbons from the catalyst, (v) transporting stripped catalyst from the stripper to a catalyst regenerator; (vi) regenerating stripped catalyst by contact with oxygen containing gas to produce regenerated catalyst; and (vii) recycling the regenerated catalyst to the cracking zone to contact further quantities of heavy hydrocarbon feed, the improvement which comprises reducing the sulfur content of a the gasoline portion of the liquid cracking products, by catalytically cracking the feed fraction at elevated temperature in the presence of a product sulfur reduction catalyst which comprises a porous molecular sieve having (i) a first metal component which is within the interior pore structure of the molecular sieve and which comprises a metal in an oxidation state greater than zero and (ii) a second metal component which is within the interior pore structure of the molecular sieve and which comprises at least one rare earth.
 10. A method according to claim 11 in which the cracking catalyst comprises a matrixed faujasite zeolite.
 11. A method according to claim 12 in which the product sulfur reduction catalyst comprises a large pore size or intermediate pore size zeolite as the molecular sieve component, vanadium as the first metal component and a combination of cerium and at least one other rare earth metal as the second metal component.
 12. A method according to claim 13 in which the large pore size zeolite of the product sulfur reduction catalyst comprises zeolite USY.
 13. A catalytic composition which comprises (i) a porous molecular sieve component, (ii) a first metal component comprising a metal in an oxidation state greater than zero located within the interior pore structure of the porous molecular sieve component and (ii) a second metal component comprising a rare earth metal located within the interior pore structure of the porous molecular sieve component.
 14. A catalytic composition according to claim 13 in which the porous molecular sieve component comprises a porous hydrocarbon cracking sieve component.
 15. A catalytic composition according to claim 14 in which the porous molecular sieve component comprises zeolite USY having a UCS of from 2.420 to 2.455 nm and a bulk silica:alumina ratio of at least 5.0.
 16. A catalytic composition according to claim 15 in which the porous molecular sieve component comprises zeolite USY having a UCS of from 2.420 to 2.435 nm and a bulk silica:alumina ratio of at least 5.0.
 17. A catalytic composition according to claim 13 which contains from 0.2 to 5 weight percent vanadium as the first metal component, based on the weight of the zeolite, of the first metal component.
 18. A catalytic composition according to claim 13 which comprises as the second metal component, a combination of cerium and at least one other rare earth.
 19. A catalytic composition according to claim 13 in which the metal components have has been introduced into the zeolite as exchanged cationic species within the zeolite pores.
 20. A catalytic composition according to claim 13 which is formulated as a fluidizable catalytic cracking product sulfur reduction catalyst additive having a particle size of from 20 to 100 microns, for reducing the sulfur content of a catalytically cracked gasoline fraction during the catalytic cracking process.
 21. A catalytic composition according to claim 13 which is formulated as an integrated fluidizable catalytic cracking/product sulfur reduction catalyst for cracking a heavy hydrocarbon feed to produce liquid cracking products including gasoline and reducing the sulfur content of the catalytically cracked gasoline fraction during the catalytic cracking process, which comprises fluidizable particles having a size ranging from about 20 to about 100 microns of a hydrocarbon cracking component which comprises a zeolitic molecular sieve which contains the first metal component located within the pore structure of the zeolite and the second metal component.
 22. An integrated fluidizable catalytic cracking/product sulfur reduction catalyst according to claim 21 which contains from 0.1 to 5 weight percent, based on the weight of the zeolite, of vanadium as the first metal component.
 23. An integrated fluidizable catalytic cracking product sulfur reduction catalyst according to claim 21 in which the second metal component comprises a combination of cerium and at least one other rare earth in an amount from 1 to 5 weight percent of the catalyst.
 24. An integrated fluidizable catalytic cracking product sulfur reduction catalyst according to claim 21 in which the zeolitic molecular sieve comprises zeolite USY having a UCS of from 2.420 to 2.455 nm and a bulk silica:alumina ratio of at least 5.0.
 25. A fluidizable catalytic cracking product sulfur reduction catalyst composition according to claim 24 in which the porous molecular sieve component comprises zeolite USY having a UCS of from 2.420 to 2.435 nm and a bulk silica:alumina ratio of at least 5.0. 